We present a cation-exchange approach for tunable A-site alloys of cesium (Cs + ) and formamidinium (FA + ) lead triiodide perovskite nanocrystals that enables the formation of compositions spanning the complete range of Cs 1- x FA x PbI 3 , unlike thin-film alloys or the direct synthesis of alloyed perovskite nanocrystals. These materials show bright and finely tunable emission in the red and near-infrared range between 650 and 800 nm. The activation energy for the miscibility between Cs + and FA + is measured (∼0.65 eV) and is shown to be higher than reported for X-site exchange in lead halide perovskites. We use these alloyed colloidal perovskite quantum dots to fabricate photovoltaic devices. In addition to the expanded compositional range for Cs 1- x FA x PbI 3 materials, the quantum dot solar cells exhibit high open-circuit voltage ( V OC ) with a lower loss than the thin-film perovskite devices of similar compositions.
In this work, a comparative study on the supramolecular assemblies formed by calixpyridinium and two alginates with different viscosities was performed. We found that sodium alginate (SA) with medium viscosity (SA-M) had a better capability to induce aggregation of calixpyridinium in comparison with SA with low viscosity (SA-L) because of the stronger electrostatic interactions between calixpyridinium and SA-M. Therefore, the morphology of calixpyridinium-SA-M supramolecular aggregates was a compact spherical structure, while that of calixpyridinium-SA-L supramolecular aggregates was an incompact lamellar structure. As a result, adding much more amount of 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt to calixpyridinium-SA-M solution was required to achieve the balance of the competitive binding, and in comparison with calixpyridinium-SA-L supramolecular aggregates, calixpyridinium-SA-M supramolecular aggregates were more sensitive to alkali. However, for the same reason, in comparison with calixpyridinium-SA-M supramolecular aggregates, calixpyridinium-SA-L supramolecular aggregates were much more stable in water not only at room temperature but also at a higher temperature, and even in salt solution. Therefore, in comparison with calixpyridinium-SA-L supramolecular aggregates, calixpyridinium-SA-M supramolecular aggregates exhibited a completely opposite response to acid because of the generation of salt. Because SA is an important biomaterial with excellent biocompatibility, it is anticipated that this comparative study is extremely important in constructing functional supramolecular biomaterials.
This paper discusses the influence of reactor design and initial consistency when partially hydrolyzing microcrystalline cellulose (MCC) in supercritical water. Experiments conducted on two pilot reactors located in Finland and in Spain showed that stopping the reaction using depressurization instead of quenching, combined with a sufficiently high MCC consistency, led to significant change in reaction kinetics. A complete particle size reduction was achieved after 50 ms only due to additional shear-induced degradation, with a low-molecular-weight product yield above 50 wt % and an average DP of 25. In addition, gradually increasing the MCC consistency triggered precipitation under higher apparent temperature, which affected both the morphology and structure of the product. A range of particles from ribbon-like cellulose II to shish-kebab structures to lamellar cellulose IVII crystals was obtained. Furthermore, heat requirements as low as 66 kJ·g–1 of product confirm the high potential and versatility of t...
A series of 3-hydroxyflavone (3-HF) ESIPT (excited-state intramolecular proton transfer) boronate-based fluorescent probes have been developed for the detection of peroxynitrite (ONOO - ). The dyes are environmentally sensitive, and each probe exhibited a ratiometric response toward ONOO - in a micellar environment. The probes were used to image different aggregation states of amyloid-β (Aβ) in the presence of ONOO - . The 3-HF-OMe probe was found to produce a ratiometric response toward ONOO - when bound to Aβ aggregates, resulting in a novel host-guest ensemble, which adds insight into the development of other ESIPT-based probes for the simultaneous sensing of fibrous proteins/peptides and environmental ROS/RNS.
The present work investigates variations in the relative strengths of average premidnight and postmidnight aurorae. The average auroral energy flux data for the southern hemisphere in 2004–2015 are taken from the Special Sensor Ultraviolet Spectrographic Imager onboard the Defense Meteorological Satellite Program F16 satellite. The main findings are as follows: (1) In local winter, the maximum auroral energy flux over the oval is located in the premidnight sector (18:00–00:00 magnetic local time) under geomagnetically quiet condition (Kp = 1) and moves toward the postmidnight sector (00:00–06:00 magnetic local time) as the Kp index increases. (2) In local summer, the maximum energy flux occurs in the postmidnight for higher solar activities (F10.7 > 100 sfu). (3) The premidnight bulge of the auroral energy flux is most prominent under winter, solar minimum and geomagnetically quiet (Kp = 1) conditions. (4) Relatively more auroral energy tends to be deposited in the postmidnight sector than in the premidnight sector as Kp increases. These results show that the auroral energy over the nightside oval is redistributed on average as the season, solar flux, and geomagnetic activity change. This would substantially affect the thermosphere and ionosphere at high latitudes.
Temperature variation has been proposed to play an important role in the formation of the sporadic sodium layers (SSLs or Na S ) in subtropic area, based on the observed significant correlation between SSLs and high temperatures. The icy‐dust particle, which could form in the extremely cold conditions and act as absorbers of sodium species, was proposed to be a possible candidate for the sodium reservoir of the SSLs. In this study, the University of Science and Technology of China temperature/wind lidar and the sodium fluorescence lidar at a subtropic station Hefei (31°N, 117°E), China, were used to observe sodium density, temperature, and wind profiles simultaneously throughout the SSL events. Based on the observations of two SSLs occurring on 12 and 13 May 2013, the possibility of an icy‐dust layer existing and acting as the sodium reservoir is tested for the first time in details. Both events experienced an extremely cold temperature (40 K). An empirical model including two main steps is then proposed: first, sodium species are collected by an icy‐dust reservoir and stored during the extremely cold phase; second, free sodium atoms could be released from the reservoir by a possible trigger. As a result, this kind of SSLs could possibly be regarded as a quasi‐continuous phenomenon caused and modulated by temperature variations with an icy‐dust model that can exhibit intermittent time variations related to the water vapor concentration.
In this study, multiple data sets from Beidou geostationary orbit satellites total electron contents (TECs), ionosonde, meteor radar, magnetometer, and model simulations have been used to investigate the ionospheric responses in the Asian‐Australian sector during the September 2017 geomagnetic storm. It was found that long‐duration daytime TEC enhancements that lasted from 7 to 12 September 2017 were observed by the Beidou geostationary orbit satellite constellation. This is a unique event as the prominent TEC enhancements persisted during the storm recovery phase when geomagnetic activity became quiet. The Thermosphere‐Ionosphere Electrodynamics Global Circulation Model predicted that the TEC enhancements on 7–9 September were associated with the geomagnetic activity, but it showed significant electron density depletions on 10 and 11 September in contrast to the observed TEC enhancements. Our results suggested that the observed long‐duration TEC enhancements from 7 to 12 September are mainly associated with the interplay of ionospheric dynamics and electrodynamics. Nevertheless, the root causes for the observed TEC enhancements seen in the storm recovery phase are unknown and require further observations and model studies.
The response of the mesospheric migrating diurnal (DW1) tide to the Madden‐Julian oscillation (MJO) is investigated for the first time using a simulation from the Specified‐Dynamic Whole Atmosphere Community Climate Model (SD‐WACCM), which is driven by reanalysis data. Analysis shows that a significant connection exists between the MJO and the mesospheric DW1 tidal amplitude. During MJO phases 2 and 3, the convection anomalies are associated with enhancement in both the solar insolation absorption and latent heat release in the equatorial troposphere; these in turn lead to stronger DW1 forcing. Conversely, the forcing of DW1 by solar and latent heating in the troposphere is weaker during MJO phase 8. The difference of the tidal amplitude during the opposite MJO phases from the boreal winter mean state is ~15–20%. The parameterized gravity wave variations are found to have a significant impact on the DW1 tidal response in some phases of the MJO.